1. Field of the Invention
This invention relates generally to apparatus for reproducing digital signals and, more particularly, is directed to improvements in apparatus of the rotary head type for reproducing digital signals recorded on magnetic or other recording tape.
2. Description of the Prior Art
Apparatus for recording and reproducing digital signals is known in which an audio or other analog signal is converted to digital signals which, along with digital signals indicating an address along the tape, a program number and the like, are recorded by a rotary head on a magnetic tape that is being transported at a normal tape speed. The digital signals thus recorded are reproduced from the tape transported at the normal speed by means of the rotary head scanning the tape, and the reproduced digital signals are converted to the corresponding audio or other analog signal, while the reproduced address, program number and the like are available for identifying the audio or other analog signal being reproduced. An example of apparatus for recording and reproducing digital signals is disclosed in detail in European Patent Application No. 0092403, filed by the assignee of the present application and published on Oct. 26, 1983.
In recording and reproducing apparatus of the described type, the tape is transported at a high speed, for example, in the fast-forward and fast-rewind modes of operation, when searching for a particular recorded program that is to be played back or reproduced. Even when the tape is thus transported at a high speed, it is desirable that the portion of the recorded digital signals indicating the address and program number be reproduced by the rotary head for use in indicating the position of the tape and for controlling the transport or drive of the latter. However, if the rotary head is rotated at the normal rotational speed when the tape is being transported at high speed, the relative speed between the rotary head and the transported tape will be different from the relative speed therebetween in the normal playback mode, and it becomes difficult to reproduce the digital signals recorded on the tape.
In U.S. patent application Ser. No. 06/791,518, filed by the present inventors on Oct. 25, 1985, and having an assignee in common herewith, there is disclosed an apparatus for reproducing digital signals recorded on a tape and in which, when the tape is transported at a high speed, the rotational speed of the rotary head is suitably controlled so that the relative speed between the rotary head and the tape remains substantially equal to that in the normal playback mode. In the foregoing apparatus, the rotary head is rotated in the same direction for the normal playback mode, the fast-forward mode and the fast-rewind mode. In order to make the relative speed between the rotary head and the tape in the rewind mode equal to such relative speed in the normal playback mode, it is necessary to substantially reduce the rotational speed of the rotary head as compared with its rotational speed for the normal playback mode. However, if the rotational speed of the rotary head is substantially decreased, the rotation of the motor driving the rotary head becomes unstable, and the output from a detecting device, such as, a frequency or pulse generator, for indicating the rotational phase of the rotary head, also becomes unstable. Accordingly, the absolute tape speed in the fast-rewind mode is limited in the above-described apparatus.